Electric motor pole position sensing method, pole position sensing apparatus, and electric motor control apparatus using the same

ABSTRACT

It is an object of the invention to provide a method which can detect a magnetic pole position easily and surely by using high-frequency currents such as harmonics of an inverter output and carrier frequency components.  
     In the invention, an arbitrary high frequency other than an output frequency of a voltage source PWM inverter is generated in input voltages or currents of a motor by means ( 6 ) for producing an arbitrary phase difference between respective two phases such as UV, VW, or WU in the inverter ( 7 ), the voltages or currents are converted to a two-phase stationary coordinate system in which U-phase of the motor is α-axis and an axis intersecting the axis at 90 deg. is β-axis, a current of the arbitrary high-frequency component is detected in each of the α- and β-axes, the voltages or currents are converted to a two-phase stationary coordinate system in which a phase is shifted by 45 deg. from the two-phase stationary coordinate system, or in which an axis that is shifted by 45 deg. from the α-axis is α′-axis and an axis intersecting the axis at 90 deg. is β′-axis, a current of the arbitrary high-frequency component is detected in each of the α′- and β′-axes, and a magnetic pole position of the motor is detected ( 12 ) by using the high-frequency current components that are detected respectively in the four axes.

TECHNICAL FIELD

[0001] The present invention relates to an apparatus for controlling amotor which accurately estimates a magnetic pole position at a very lowspeed including zero speed, and which controls the torque and the speedon the basis of the estimated magnetic pole position.

BACKGROUND ART

[0002] As a conventional method of estimating a magnetic pole position,widely used is a method in which an induced voltage that is proportionalto a motor speed is calculated from a motor input voltage and a current,such as that reported in “Adaptive Current Control Method for BrushlessDC motor with Function of Parameter Identification” IEEJ Transactions onIndustry Applications, Vol. 108 No. 12, 1988. Also known is “Zero SpeedTorque Control of Sensorless Salient-Pole Synchronous Motor” 1996National Convention of IEEJ Industry Applications Society No. 170. Inthis technique, an AC signal is superimposed on a voltage command value,and a detected current is FFT analyzed to detect the rotational speed ofa motor and a magnetic pole position. However, a method, which estimatesthe speed and position of a rotor on the basis of an induced voltage ofa motor, operates with sufficient accuracy in a high speed region, butcannot perform correct estimation at a very low speed from which littleinformation of the induced voltage is obtained.

[0003] Therefore, several methods have been proposed in which an ACsignal that has no relation to a driving frequency, and that is used forsensing is injected into a motor, and a rotor position is estimated fromrelationships between the voltage and the current. However, a specialsignal generator is necessary in order to inject such a sensing signal,thereby causing a problem in that the control is complicated. Othermethods in which a special sensing signal is not injected and a magneticpole position is detected by using harmonics of an inverter output orcurrents of carrier frequency components are reported in “PositionSensorless IPM Motor Drive System Using Position Estimation Method Basedon Saliency” IEEJ Transactions on Industry Applications, Vol. 118 No. 5,1998, and “Carrier Frequency Component Method for Position SensorlessControl of IPM Motor in Lower Speed Range” IEEJ Transactions on IndustryApplications, Vol. 120 No. 2, 2000.

[0004] The former method is characterized in that an inductance iscalculated from high-frequency currents generated by output voltageharmonics of a PWM inverter, and the position is detected on the basisof the inductance. The latter method is characterized in that a phasedifference of 120 deg. is produced between PWM inverter carrier signalsof two of three or U-, V-, and W-phases to generate voltages andcurrents of carrier frequency components other than the drivingfrequency, and the position is detected by using only the carrierfrequency component currents based on the assumption that a voltageduring the carrier period is constant.

[0005] The methods which detect a magnetic pole position by usingharmonics of an inverter output or high-frequency currents of carrierfrequency components have an advantage that a special sensing signalgenerator is not necessary. However, the methods require plural currentdetections during the carrier period. Therefore, a special currentdetecting circuit is required, and synchronization between the currentdetection timing and the position calculation is complicated.Consequently, it is difficult to practically use such methods.

[0006] It is an object of the invention to provide a method of detectinga magnetic pole position of a motor and an apparatus for detecting amagnetic pole position in which, although high-frequency currents ofcarrier frequency components or the like are used, a special currentdetecting circuit is not required, and synchronization between thecurrent detection timing and the position calculation can be easilyattained, and also to provide an apparatus for controlling a motor usingthe same.

DISCLOSURE OF THE INVENTION

[0007] In order to attain the object, the invention of claim 1 providesa method of detecting a magnetic pole position of a motor havingelectric saliency wherein an arbitrary high frequency other than anoutput frequency of a voltage source PWM inverter is generated in inputvoltages or currents of a motor by means for producing an arbitraryphase difference between respective two phases such as WV, VW, or WU inthe inverter, the voltages or currents are converted to a two-phasestationary coordinate system in which U-phase of three phases of themotor is α-axis and an axis intersecting the axis at 90 deg. is β-axis,a current of the arbitrary high-frequency component is detected in eachof the α- and β-axes, the voltages or currents are converted to atwo-phase stationary coordinate system in which a phase is similarlyshifted by 45 deg. from the two-phase stationary coordinate system, orin which an axis that is shifted by 45 deg. from the α-axis is α′-axisand an axis intersecting the axis at 90 deg. is β′-axis, a current ofthe arbitrary high-frequency component is detected in each of the α′-and β′-axes, and a magnetic pole position of the motor is detected byusing the high-frequency current components that are detectedrespectively in the four axes.

[0008] The invention of claim 2 is characterized in that, in the methodof detecting a magnetic pole position of a motor according to claim 1,the magnetic pole position of the motor is detected by using an outputwhich is obtained by extracting peak currents from the high-frequencycurrent components that are detected respectively in the four axes, andthen passing the peak currents through a low-pass filter.

[0009] The invention of claim 3 provides an apparatus for detecting amagnetic pole position for a controlling apparatus for driving a motorby a voltage source PWM inverter wherein the apparatus comprises: meansfor producing an arbitrary phase difference in PWM carrier signalsbetween respective two phases such as UV, VW, or WU of three or U-, V-,and W-phases; means for extracting high-frequency voltages andhigh-frequency currents that are generated by it, from detected voltagesor a command voltage and detected currents; and means for detecting amagnetic pole position by using the extracted high-frequency voltagesand currents.

[0010] The invention of claim 4 provides an apparatus for detecting amagnetic pole position for a controlling apparatus for driving a motorby a voltage source PWM inverter wherein the apparatus comprises: meansfor producing an arbitrary phase difference in PWM carrier signalsbetween respective two phases such as UV, VW, or WU of three or U-, V-,and W-phases; means for extracting only high-frequency currents that aregenerated by it; and means for detecting a magnetic pole position byusing the extracted high-frequency currents.

[0011] The invention of claim 5 is characterized in that, in theapparatus for detecting a magnetic pole position of a motor according toclaim 4, the method of detecting a magnetic pole position according toclaim 1 is used as the means for detecting a magnetic pole position.

[0012] The invention of claim 6 is characterized in that, in theapparatus for detecting a magnetic pole position of a motor according toclaim 4, the method of detecting a magnetic pole position according toclaim 2 is used as the means for detecting a magnetic pole position.

[0013] The invention of claim 7 is characterized in that the arbitraryphase difference is 120 deg., and the arbitrary high frequency is aninverter carrier frequency.

[0014] The invention of claim 8 is characterized in that the arbitraryphase difference is 120 deg., and the arbitrary high frequency is aninverter carrier frequency.

[0015] The invention of claim 9 is characterized in that the arbitraryphase difference is 120 deg., and the arbitrary high frequency is aninverter carrier frequency.

[0016] The invention of claim 10 is characterized in that an apparatuscomprises a current controlling apparatus which splits a detectedcurrent into a pole direction component and a torque component by usingthe position detected by the apparatus for detecting a magnetic poleposition according to any one of claims 3 and 4, which feedbacks thecomponents to compare the components with current command values for thepole direction component and the torque component, and which implementsa current control so that deviations in the comparisons become zero.

[0017] The invention of claim 11 is characterized in that the apparatuscomprises a speed detecting apparatus which detects a speed by using theposition detected by the apparatus for detecting a magnetic poleposition according to any one of claims 3 and 4.

[0018] The invention of claim 12 is characterized in that the apparatuscomprises a speed controlling apparatus which compares the speeddetected on the basis of the speed detecting apparatus of the apparatusfor controlling a motor according to claim 11, with a command speed,which implements a speed control so that a deviation in the comparisonbecomes zero, and which outputs a torque command value or a currentcommand value corresponding to a torque command.

[0019] The invention of claim 13 is characterized in that the apparatuscomprises a position controlling apparatus which compares the magneticpole position detected on the basis of the apparatus for detecting amagnetic pole position according to any one of claims 3 and 4, with acommand position, which implements a position control so that adeviation in the comparison becomes zero, and which outputs a speedcommand value.

[0020] The invention of claim 14 is characterized in that the apparatuscomprises a torque controlling apparatus having: the apparatus fordetecting a magnetic pole position according to claim 9; and the currentcontrolling apparatus according to claim 10.

[0021] The invention of claim 15 is characterized in that the apparatuscomprises a speed controlling apparatus having: the apparatus fordetecting a magnetic pole position according to claim 9; the currentcontrolling apparatus according to claim 10; the speed detectingapparatus according to claim 11, and the speed controlling apparatusaccording to claim 12.

[0022] The invention of claim 16 is characterized in that the apparatuscomprises a position controlling apparatus having: the apparatus fordetecting a magnetic pole position according to claim 9; the currentcontrolling apparatus according to claim 10; the speed detectingapparatus according to claim 11, the speed controlling apparatusaccording to claim 12; and the position controlling apparatus accordingto claim 13.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIGS. 1(a) to 1(c) show the illustration views of the principleof the method of detecting a magnetic pole position of a motor accordingto the invention.

[0024]FIG. 2 is a control block diagram of an apparatus for detecting amagnetic pole position of a motor shown in FIG. 1.

[0025]FIG. 3 is a block diagram of a PWM controller shown in FIG. 2.

[0026]FIG. 4 is a diagram showing the configuration of a pole positiondetector shown in FIG. 2.

[0027] In the figures, the reference numeral 1 denotes a speedcontroller, 2 denotes a q-axis current controller, 3 denotes anoninterference controller, 4 denotes a d-axis current controller, 5denotes a voltage amplitude and phase calculator, 6 denotes a PWMcontroller, 6-1 denotes a three-phase voltage command calculator, 6-2denotes a comparator, 6-3 denotes a phase shifter, 6-4 denotes a carriersignal generator, 7 denotes an inverter main circuit, 8 denotes an ACmotor, 9 denotes a stationary coordinate converter, 10 denotes arotating coordinate converter, 11 denotes a band-pass filter, 12 denotesa pole position detector, 13 denotes a speed calculator, 14 denotes acoordinate converter, 15 denotes an absolute value calculator, 16denotes a low-pass filter, and 17 denotes a pole position calculator.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] First, the invention is based on a method of detecting a magneticpole position by using a current of a carrier frequency component, andthe basic principle of the magnetic pole position detection will bedescribed. In a vector controlling apparatus for a synchronous motorwhich is driven by a voltage source PWM inverter, an arbitrary phasedifference is produced between PWM carrier signals of respective twophases such as UV, VW, or WU of three or U-, V-, and W-phases, therebygenerating high-frequency voltages and high-frequency currents that aredifferent from a driving frequency. Namely, the frequency band ofgenerated high-frequency components can be adjusted to a frequencydifferent from the driving frequency by arbitrarily giving thefrequencies of the PWM carriers and the phase difference of thecarriers. When the phase difference is 120 deg., for example, voltageand current components the frequencies of which are equal to the carrierfrequency largely appear. In this case, the high-frequency voltages canbe expressed by the following expression: $\begin{bmatrix}u_{uh} \\u_{vh} \\u_{wh}\end{bmatrix} = \begin{bmatrix}{{Vsin}\quad \left( {\omega_{h}t} \right)} \\{{Vsin}\left( {{\omega_{h}t} - {2{\pi/3}}} \right)} \\{{Vsin}\left( {{\omega_{h}t} + {2{\pi/3}}} \right)}\end{bmatrix}$

[0029] where uuh, uvh, and uwh indicate high-frequency voltages of theU-, V-, and W-phases, respectively, V indicates the amplitude of ahigh-frequency voltage, and ω_(h) indicates a carrier angular frequency.

[0030] Furthermore, relationships between the high-frequency voltagesand the high-frequency currents are expressed by following expression(1): $\begin{matrix}{\begin{bmatrix}u_{uh} \\u_{vh} \\u_{wh}\end{bmatrix} = {\begin{bmatrix}L_{uu} & L_{uv} & L_{vw} \\L_{vu} & L_{vv} & L_{vw} \\L_{wu} & L_{wv} & L_{ww}\end{bmatrix}{\frac{\quad}{t}\begin{bmatrix}i_{uh} \\i_{vh} \\i_{wh}\end{bmatrix}}}} & (1)\end{matrix}$

[0031] where iuh, ivh, and iwh indicate high-frequency currents of theU-, V-, and W-phases, respectively, L indicates an inductance, Luu, Lvv,and Lww indicate self inductances of the U-, V-, and W-phases,respectively, and the others indicate phase-to-phase inductances. Amotor in which a permanent magnet is used in a rotor has electricsalient poles (this means that the d-axis inductance and the q-axisinductance are different from each other). Therefore, the inductancescontain information of a magnetic pole position.

L _(uv) =−L _(go)/2+L _(g2) cos(2θ−2π/3)

L _(vw) =−L _(g0)/2+L _(g2) cos(2θ)

L _(uw) =−L _(g0)/2 +L _(g2) cos(2θ+2π/3)

L _(uu) =L _(s) +L _(g0) +L _(g2) cos(2θ)

L _(vv) =L _(s) +L _(g0) +L _(g2) cos(2θ+2π/3)

L _(ww) =L _(s) +L _(g0) +L _(g2) cos(2θ−2π/3)

[0032] where Lg0 indicates the magnetizing inductance in the air gapflux, Ls indicates the leakage inductance of a stator, and Lg2 indicatesan inductance the degree of which depends on the angle.

[0033] When expression (1) is converted to a stator-based stationarycoordinate system, following expression (2) is obtained: $\begin{matrix}{\begin{bmatrix}u_{\alpha \quad h} \\u_{\beta \quad h}\end{bmatrix} = {\begin{bmatrix}{L_{0} + {L_{1}\cos \quad \left( {2\theta} \right)}} & {L_{1}{\sin \left( {2\theta} \right)}} \\{L_{1}{\sin \left( {2\theta} \right)}} & {L_{0} - {L_{1}{\cos \left( {2\theta} \right)}}}\end{bmatrix}{\frac{\quad}{t}\begin{bmatrix}i_{\alpha \quad h} \\i_{\beta \quad h}\end{bmatrix}}}} & (2)\end{matrix}$

[0034] where L0=Ls+3Lg0/2, and L1=3Lg2/2.

[0035] From expression (2), magnetic pole position information sin(2θ)and cos(2θ) are derived: $\begin{matrix}\begin{matrix}{\begin{bmatrix}{\cos \quad \left( {2\theta} \right)} \\{\sin \left( {2\theta} \right)}\end{bmatrix} = \frac{1}{L_{1}\left\lbrack {\left( {\frac{\quad}{t}i_{\alpha \quad h}} \right)^{2} + \left( {\frac{\quad}{t}i_{\beta \quad h}} \right)^{2}} \right\rbrack}} \\{\quad \begin{bmatrix}{{u_{\alpha \quad h}\frac{\quad}{t}i_{\alpha \quad h}} - {u_{\beta \quad h}\frac{\quad}{t}i_{\beta \quad h}} - {L_{0}\left\lbrack {\left( {\frac{\quad}{t}i_{\alpha \quad h}} \right)^{2} - \left( {\frac{\quad}{t}i_{\beta \quad h}} \right)^{2}} \right\rbrack}} \\{{u_{\alpha \quad h}\frac{\quad}{t}i_{\beta \quad h}} + {u_{\beta \quad h}\frac{\quad}{t}i_{\alpha \quad h}} - {2{L_{0}\left( {\frac{\quad}{t}i_{\alpha \quad h}\frac{\quad}{t}i_{\beta \quad h}} \right)}}}\end{bmatrix}}\end{matrix} & (3)\end{matrix}$

[0036] In this way, the magnetic pole position can be estimated by usingthe high-frequency voltages and the high-frequency currents.

[0037] When the estimation mechanism is synchronized with the carrierfrequency and the current is sampled at a point where a high-frequencycurrent iβ_(h) reaches a peak, iα_(h) which is separated in phase by 90deg. is substantially zero. Therefore, expression (3) can be expressedin a simpler manner as following expression (4): $\begin{matrix}{\begin{bmatrix}{\cos \left( {2\theta} \right)} \\{\sin \left( {2\theta} \right)}\end{bmatrix} = {{\frac{1}{{L_{1}\left( {\frac{\quad}{t}i_{\beta \quad h}} \right)}^{2}}\begin{bmatrix}{{{- u_{\beta \quad h}}\frac{\quad}{t}i_{\beta \quad h}} + {L_{0}\left( {\frac{\quad}{t}i_{\beta \quad h}} \right)}^{2}} \\{u_{\alpha \quad h}\frac{\quad}{t}i_{\beta \quad h}}\end{bmatrix}} = \begin{bmatrix}\frac{- u_{\beta \quad h}}{\left( {L_{1}\frac{\quad}{t}i_{\beta \quad h}} \right) + L_{0}} \\\frac{u_{\alpha \quad h}\quad}{\left( {L_{1}\frac{\quad}{t}i_{\beta \quad h}} \right)}\end{bmatrix}}} & (4)\end{matrix}$

[0038] From expressions (3) and (4) above, cos(2θ) and sin(2θ) areobtained, the value of the angle 2θ is obtained on the basis of theinformation values from a table of trigonometric functions which ispreviously prepared in a calculator, and the value is divided by 2,whereby the magnetic pole position θ (hereinafter) can be detected. Inthe calculations of expressions (3) and (4), current differentiationvalues are used. At a high speed, the currents are rapidly changed, andhence the magnetic pole position is vibratory. From expression (2),therefore, current differentiation values are obtained as shown inexpression (5). When both sides are integrated, expression (6) isobtained. $\begin{matrix}{{\frac{\quad}{t}\begin{bmatrix}i_{\alpha \quad h} \\i_{\beta \quad h}\end{bmatrix}} = {{\frac{1}{L_{0}^{2} - L_{1}^{2}}\begin{bmatrix}{L_{0} - {L_{1}{\cos \left( {2\theta} \right)}}} & {{- L_{1}}{\sin \left( {2\theta} \right)}} \\{{- L_{1}}{\sin \left( {2\theta} \right)}} & {L_{0} + {L_{1}\cos \quad \left( {2\theta} \right)}}\end{bmatrix}}\begin{bmatrix}u_{\alpha \quad h} \\u_{\beta \quad h}\end{bmatrix}}} & (5) \\{\begin{bmatrix}i_{\alpha \quad h} \\i_{\beta \quad h}\end{bmatrix} = {{\frac{1}{L_{0}^{2} - L_{1}^{2}}\begin{bmatrix}{L_{0} - {L_{1}{\cos \left( {2\theta} \right)}}} & {{- L_{1}}{\sin \left( {2\theta} \right)}} \\{{- L_{1}}{\sin \left( {2\theta} \right)}} & {L_{0} + {L_{1}\cos \quad \left( {2\theta} \right)}}\end{bmatrix}}\begin{bmatrix}{\int\quad {u_{\alpha \quad h}{t}}} \\{\int\quad {u_{\beta \quad h}{t}}}\end{bmatrix}}} & (6)\end{matrix}$

[0039] From expression (6), the magnetic pole position informationsin(2θ) and cos(2θ) are derived: $\begin{matrix}\begin{matrix}{\begin{bmatrix}{\cos \left( {2\theta} \right)} \\{\sin \left( {2\theta} \right)}\end{bmatrix} = {\frac{1}{L_{1}\left( {\left( {\int\quad {u_{\alpha \quad h}{t}}} \right)^{2} + \left( {\int\quad {u_{\beta \quad h}{t}}} \right)^{2}} \right)} \cdot}} \\{\quad \begin{bmatrix}{{L_{0}\left( {\int\quad {u_{\alpha \quad h}{t}}} \right)}^{2} - \left( {\int\quad {u_{\beta \quad h}{t}}} \right)^{2} - \left( {L_{0}^{2} - L_{1}^{2}} \right)} & \left( {{i_{\alpha \quad h}{\int\quad {u_{\alpha \quad h}{t}}}} - {i_{\beta \quad h}{\int\quad {u_{\beta \quad h}{t}}}}} \right) \\{{2L_{0}{\int{u_{\alpha \quad h}{1}{\int{u_{\beta \quad 1}{t}}}}}} - \left( {L_{0}^{2} - L_{1}^{2}} \right)} & \left( {{i_{\alpha \quad h}{\int\quad {u_{\beta \quad h}{t}}}} + {i_{\beta \quad h}{\int\quad {u_{\alpha \quad h}{t}}}}} \right)\end{bmatrix}}\end{matrix} & (7)\end{matrix}$

[0040] In the case where the carrier period is synchronized with thevoltage sampling period, the voltage integration value is dealt as afixed value as in the following expression. In an inverter of a usualcontrol voltage source, the voltage integration value is a fixed valueduring the carrier period.

∫u_(αh)dt=u_(αh)Δt, ∫u_(βh)dt=u_(βh)Δt

[0041] Δt: sampling time

[0042] When uαh is a peak voltage, uβh=0. At this timing, therefore,cos(2θ) is calculated from expression (7) as follow:${\cos \left( {2\theta} \right)} = {\frac{L_{0}}{L_{1}} - {\frac{\left( {L_{0}^{2} - L_{0}^{2}} \right)}{L_{1}} \cdot \frac{\left. i_{\alpha \quad h} \right|_{\theta = {0{^\circ}}}}{\left. u_{\alpha \quad h} \middle| {}_{\theta = {0{^\circ}}}{{\cdot \Delta}\quad t} \right.}}}$

[0043] When uβh is a peak voltage, uαh=0. At this timing, therefore,cos(2θ) is calculated from expression (7) as follow: $\begin{matrix}{{\cos \quad \left( {2\theta} \right)} = {{- \frac{L_{0}}{L_{1}}} + {\frac{\left( {L_{0}^{2} - L_{1}^{2}} \right)}{L_{1}} \cdot \frac{\left. i_{\beta \quad h} \right|_{\theta = {90{^\circ}}}}{\left. u_{\beta \quad h} \middle| {}_{\theta = {90{^\circ}}}{{\cdot \Delta}\quad t} \right.}}}} & (8)\end{matrix}$

[0044] At the point where θ is advanced by 45 deg. from the point ofuαh=0, uαh=uβh. At this timing, therefore, sin(2θ) is calculated fromexpression (7) as follow: $\begin{matrix}{{\sin \left( {2\theta} \right)} = {\frac{L_{0}}{L_{1}} - {\frac{\left( {L_{0}^{2} - L_{1}^{2}} \right)}{L_{1}} \cdot \frac{\left. \left( {i_{\alpha \quad h} + i_{\beta \quad h}} \right) \right|_{\theta = {45{^\circ}}}}{\left. \left( {u_{\alpha \quad h} + u_{\beta \quad h}} \right) \middle| {}_{\theta = {45{^\circ}}}{{\cdot \Delta}\quad t} \right.}}}} & (9)\end{matrix}$

[0045] At the point where θ is advanced by 135 deg. from the point ofuαh=0, uαh=−uβh. At this timing, therefore, sin(2θ) is calculated fromexpression (7) as follow: $\begin{matrix}{{\sin \quad \left( {2\theta} \right)} = {{- \frac{L_{0}}{L_{1}}} + {\frac{\left( {L_{0}^{2} - L_{0}^{2}} \right)}{L_{1}} \cdot \frac{\left. \left( {i_{\alpha \quad h} - i_{\beta \quad h}} \right) \right|_{\theta = {135{^\circ}}}}{\left. \left( {u_{\alpha \quad h} + u_{\beta \quad h}} \right) \middle| {}_{\theta = {135{^\circ}}}{{\cdot \Delta}\quad t} \right.}}}} & (10)\end{matrix}$

[0046] As a result, it is possible to detect the position of themagnetic pole. In order to realize this method of detecting a magneticpole position, however, the high-frequency currents at the timings ofuαh=0 and uαh=uβh must be correctly detected, and hence this techniqueis hardly performed in a practical use. In the invention, therefore, thefollowing modification is applied to solve the problem.

[0047]FIG. 1 shows the principle of the detection of a magnetic poleposition according to the invention. When, as shown in FIG. 1(a), atwo-phase stationary coordinate system in which the U-phase of the threephases of the motor is α-axis and an axis intersecting the axis at 90deg. is t-axis is set, and a two-phase stationary coordinate system inwhich an axis that is shifted by 45 deg. from the α-axis is α′-axis andan axis intersecting the axis at 90 deg. is β′-axis is set, inductancesin the axes are indicated as expressions (11) to (14) below.

[0048] The inductance in the α-axis is:

L _(α)(θ)=L 0 −L ₁ cos (2θ)  (11)

[0049] In the expressions, θ, θ′, θ″, and θ′″ are variables of the phasein which the respective α-, β-, α′-, and β′-axes are zero deg.

[0050] This state is shown in FIG. 1(b) indicating that the magneticpole position coincides with the α-axis.

[0051] Assuming that the phase is advanced so that the magnetic poleposition is shifted from the α-axis by Δθ FIG. 1(c),

[0052] the inductance in the α-axis is:

L _(α) =L ₀ −L ₁ cos (−2Δθ)=L ₀ −L ₁ cos (2Δθ),  (15)

[0053] the inductance in the β-axis is:

L _(β) =L ₀ +L ₁ cos (−2Δθ)=L ₀ +L ₁ cos (2Δθ),  (16)

[0054] the inductance in the α′-axis is:

L _(α) =L ₀ +L ₁ sin (−2Δθ)=L ₀ −L ₁ sin (2Δθ),  (17)

[0055] the inductance in the β′-axis is:

L _(β) =L ₀ −L ₁ sin (−2Δθ)=L ₀ +L ₁ sin (2Δθ),  (18)

[0056] Expression (16) is subtracted from expression (15) to extractonly the magnetic pole position information as follow:

L _(α) −L _(β) =−L ₁ cos (2Δθ)  (19)

[0057] Similarly, expression (18) is subtracted from expression (17) toobtain the following:

L _(α) −L _(β) =−L ₁ sin (2Δθ)  (20)

[0058] The magnetic pole position can be detected by followingexpression (21): $\begin{matrix}{{\tan \left( {2\Delta \quad \theta} \right)} = \frac{L_{\alpha^{\prime}} - L_{\beta^{\prime}}}{L_{\alpha} - L_{\beta}}} & (21)\end{matrix}$

[0059] Hereinafter, the calculations of the inductances will bespecifically described.

[0060] In expressions (8) to (10), θ=Δθ is set. When the resultingexpressions are substituted to expressions (15) to (18), the followingsare obtained: $\begin{matrix}{L_{\alpha} = {\left( {L_{0}^{2} - L_{1}^{2}} \right) \cdot \frac{i_{\alpha \quad h}}{{u_{\alpha \quad h} \cdot \Delta}\quad t}}} & (22) \\{L_{\beta} = {{- \left( {L_{0}^{2} - L_{1}^{2}} \right)} \cdot \frac{i_{\beta \quad h}}{{u_{\beta \quad h} \cdot \Delta}\quad t}}} & (23) \\{L_{\alpha^{\prime}} = {\left( {L_{0}^{2} - L_{1}^{2}} \right) \cdot \frac{i_{\alpha^{\prime}\quad h}}{{u_{\alpha^{\prime}\quad h} \cdot \Delta}\quad t}}} & (24) \\{L_{\beta^{\prime}} = {{- \left( {L_{0}^{2} - L_{1}^{2}} \right)} \cdot \frac{i_{\beta^{\prime}\quad h}}{{u_{\beta^{\prime}\quad h} \cdot \Delta}\quad t}}} & (25)\end{matrix}$

[0061] where iα′_(h)=(iα_(h)+iβ_(h))|θ₌₄₅°,

[0062] iβ′_(h)=(iα_(h)+iβ_(h))|θ₌₁₃₅°,

[0063] uα′_(h)=(uα_(h)+uβ_(h))|θ₌₄₅°, and

[0064] uβ′_(h)=(uα_(h)+uβ_(h))|θ₌₁₃₅°.

[0065] When the voltage in the carrier period is dealt as a fixed value,the inductances can be calculated by using only the carrier frequencycomponent currents which are converted to the coordinates, respectively.Namely, the followings are obtained:

L_(α)∝|i_(αh)|_(αv)  (26)

L_(β)∝|i_(βh)|_(αv)  (27)

L_(α−)∝|i_(αh)|_(αv)  (28)

L_(β−)∝|i_(β−h)|_(αv)  (29)

[0066] where | |α_(v) indicates averaging of an absolute value.Therefore, expression (21) is reduced to: $\begin{matrix}{{\tan \quad \left( {2\Delta \quad \theta} \right)} = \frac{{i_{\alpha^{\prime}h}}_{\alpha \quad v} - {i_{\beta^{\prime}h}}_{\alpha \quad v}}{{i_{\alpha \quad h}}_{\alpha \quad v} - {i_{\beta \quad h}}_{\alpha \quad v}}} & (30)\end{matrix}$

[0067] As a result, the problem that a practical use is hardly attainedin a conventional art can be solved by, in place of calculatinginstantaneous values of carrier currents, fetching only peak values andaveraging them.

[0068] Hereinafter, an embodiment of the invention will be describedwith reference to the drawings.

[0069] FIGS. 1(a) to 1(c) show the illustration views of the principleof the method of detecting a magnetic pole position of a motor accordingto the embodiment of the invention.

[0070]FIG. 2 is a control block diagram of an apparatus for detecting amagnetic pole position of a motor shown in FIG. 1.

[0071]FIG. 3 is a block diagram of a PWM controller shown in FIG. 2.

[0072]FIG. 4 is a diagram showing the configuration of a pole positiondetector shown in FIG. 2.

[0073] Referring to FIG. 2, a speed controller 1 compares a speedcommand value with a speed estimate value, and determines a q-axiscurrent (torque current) command iqRef so that the deviation in thecomparison becomes zero. A q-axis current controller 2 compares iqRefwith a current iq which is a current proportional to the torque amongcurrents that are converted to a coordinate system 10 (a d-q coordinateconverter) rotating in synchronization with the rotor, and determines avoltage command Vq so that the deviation in the comparison becomes zero.

[0074] A d-axis current controller 4 compares idRef with a current idwhich is a current related to the magnetic pole direction among currentsthat are converted to the coordinate system rotating in synchronizationwith the rotor, and determines a voltage command Vd so that thedeviation in the comparison becomes zero. A noninterference controller 3calculates speed electromotive forces which interfere with each otherbetween the d- and q-axes, and controls them so as to cancel influenceson the current controllers. A voltage amplitude and phase calculator 5receives the voltage commands Vd, Vq, and calculates the amplitude andphase of a command voltage vector. A PWM controller 6 receives theamplitude and phase of the command voltage vector calculated by thevoltage amplitude and phase calculator 5, and generates an inverterswitching signal. The reference numeral 7 denotes an inverter maincircuit which three-phase drives an AC motor 8 by the switching signal.(The above is a vector controlling portion for a usual AC motor.)

[0075] In FIG. 2, the portion constituting the apparatus for detecting amagnetic pole position of the invention includes: a circuit whichgenerates and outputs a high frequency for detecting a magnetic poleposition, on the basis of the carrier signal of the PWM controller 6; aportion which converts three-phase high-frequency currents by astationary coordinate converter 9 (an α-βcoordinate converter), and thenconverts to the rotating coordinate system (d-q) 10; and a portion whichreceives the three-phase high-frequency currents via a BPF 11, estimatesθ by a pole position detector 12, performs detection of a magnetic poleposition to use it as a control reference, and performs speed estimationby a speed calculator 13.

[0076] Referring to FIG. 3, FIG. 3 is a detail view of the PWMcontroller 6 which generates an arbitrary high frequency. A three-phasevoltage command calculator 6-1 receives the amplitude and phase angle ofthe voltage command vector which is calculated by the usual vectorcontrolling apparatus, and calculates voltage command values of threephases.

[0077] By contrast, in order to generate high frequencies which aredifferent from a driving frequency, in carrier signals having anarbitrary frequency generated by a carrier signal generator 6-4, a phasesifter 6-3 shifts the phase of the V-phase by an angle Δθ with respectto the U-phase, and shifts the W-phase by 2Δθ, and a comparator 6-2compares the signals with the voltage command values and generatesswitching signals. The switching signals are input to the inverter maincircuit denoted by 7. (The detection of a magnetic pole position isperformed-by-using the high frequencies.)

[0078] Referring to FIG. 4, FIG. 4 is a diagram showing in detail theconfiguration of the pole position detector 12 shown in FIG. 2. Thethree-phase high-frequency currents from the BPF 11 shown in FIG. 2 areconverted by a coordinate converter 14 to the α-axis, the β-axis, theα′-axis, and the β′-axis, peak values of the converted currents arefetched, an averaging process is performed by an absolute valuecalculator 15 and a low-pass filter 16, and θ is estimated by a poleposition calculator 17.

[0079] Next, the operation will be described.

[0080] First, as shown in FIG. 3, in the carrier signals generated bythe carrier signal generator 6-4, the phase sifter 6-3 shifts the phaseof the V-phase by an angle Δθ with respect to the U-phase, and shiftsthe W-phase by 2Δθ to output the high frequencies uuh, uvh, and uwh fordetecting a magnetic pole position such as shown in expression (1).

[0081] In the estimation of a magnetic pole position, first, thestationary coordinate converter 9 extracts only an arbitrary frequencydesignated in the band-pass filter 11, with respect to a detectedvoltage or a command voltage and a detected current.

[0082] In the pole position detector 12 shown in FIG. 4, the three-phasehigh-frequency currents i output from the band-pass filter 11 areconverted by the coordinate converter 14 to the α-axis, the β-axis, theα′-axis, and the β′-axis. Then, the absolute value calculator 15implements a process of averaging peak values of the outputs (iα_(h),iβ_(h), iα′_(h), iβ′_(h)) of the coordinate converter 14. The low-passfilter 16 has an effect of more smoothing the outputs of the absolutevalue calculator 15. In the case where the number of samples of the peakvalues in the absolutizing process is large, the low-pass filter may beomitted. The outputs |iα_(h)|α_(v), |iβ_(h)|α_(v), |iα′_(h)|α_(v), and|iβ′_(h)|α_(v) of the low-pass filter 16 are proportional to theinductances of the axes as shown in expressions (26) to (29) above. Thesubsequent pole position calculator 17 calculates the magnetic poleposition from Δθ which is obtained by implementing the calculation ofexpression (30), and outputs the position. Therefore, a magnetic poleposition can be easily detected only from current values withoutcalculating inductances. Furthermore, it has been ascertained that, evenwhen the timing of current sampling is deviated by an addition of theaveraging process, an error due to the deviation scarcely occurs.

[0083] When the magnetic pole position is detected as described above,the speed estimate value ω is estimated by the speed calculator 13, adeviation with respect to ωref is adjusted by the speed controller 1,and a q-axis current component iqref is output. The q-axis currentcontroller 2 outputs the voltage command Vq which is a result ofcomparison between iqref with the current iq that is obtained byconverting the three-phase high-frequency currents to the α-β axes inthe stationary coordinate converter 9, converting a result of theconversion with respect to the d-axis by the d-q axis converter 10, andperforming a vector control synchronized with the high-frequencycurrents. The value of θ is adjusted. As a result, a motor control onthe basis of the detected magnetic pole position can be implemented.

[0084] While the invention has been described in detail with referenceto a specific embodiment, it will be understood by those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the invention.

[0085] This application is based on a Japanese patent application(JP-A-2001-238060) filed Aug. 6, 2001, and the contents of the patentapplication are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

[0086] As described above, according to the invention, inductances onfour coordinate axes can be calculated by using only carrier frequencycomponent currents which are converted to the coordinates, respectively,and calculations are conducted by using an average value obtained byfetching only peak values, in place of instantaneous values of thecarrier frequency component currents, thereby attaining an effect thatit is possible to easily solve the problem that a practical use ishardly attained in a conventional art because of complicatedsynchronization between the current detection timing and the positioncalculation.

1. A method of detecting a magnetic pole position of a motor havingelectric saliency wherein an arbitrary high frequency other than anoutput frequency of a voltage source PWM inverter is generated in inputvoltages or currents of a motor by means for producing an arbitraryphase difference between respective two phases such as V, VW, or WU insaid inverter, said voltages or currents are converted to a two-phasestationary coordinate system in which U-phase of three phases of saidmotor is α-axis and an axis intersecting said axis at 90 deg. is β-axis,a current of said arbitrary high-frequency component is detected in eachof said α- and β-axes, said voltages or currents are converted to atwo-phase stationary coordinate system in which a phase is similarlyshifted by 45 deg. from said two-phase stationary coordinate system, orin which an axis that is shifted by 45 deg. from said α-axis is α′-axisand an axis intersecting said axis at 90 deg. is β′-axis, a current ofsaid arbitrary high-frequency component is detected in each of said α′-and β′-axes, and a magnetic pole position of said motor is detected byusing said high-frequency current components that are detectedrespectively in said four axes.
 2. The method of detecting a magneticpole position of a motor according to claim 1, wherein said magneticpole position of said motor is detected by using an output which isobtained by extracting peak currents from said high-frequency currentcomponents that are detected respectively in said four axes, and thenpassing said peak currents through a low-pass filter.
 3. An apparatusfor detecting a magnetic pole position for a motor which is an apparatusfor detecting a magnetic pole position for a controlling apparatus fordriving a motor by a voltage source PWM inverter wherein said apparatuscomprises: means for producing an arbitrary phase difference in PWMcarrier signals between respective two phases such as UV, VW, or WU ofthree or U-, V-, and W-phases; means for extracting high-frequencyvoltages and high-frequency currents that are generated by it, fromdetected voltages or a command voltage and detected currents; and meansfor detecting a magnetic pole position by using said extractedhigh-frequency voltages and currents.
 4. An apparatus for detecting amagnetic pole position for a motor which is an apparatus for detecting amagnetic pole position for a controlling apparatus for driving a motorby a voltage source PWM inverter wherein said apparatus comprises: meansfor producing an arbitrary phase difference in PWM carrier signalsbetween respective two phases such as UV, VW, or WU of three or U-, V-,and W-phases; means for extracting only high-frequency currents that aregenerated by it; and means for detecting a magnetic pole position byusing said extracted high-frequency currents.
 5. The apparatus fordetecting a magnetic pole position for a motor according to claim 4,wherein the method of detecting a magnetic pole position according toclaim 1 is used as said means for detecting a magnetic pole position. 6.The apparatus for detecting a magnetic pole position for a motoraccording to claim 4, wherein the method of detecting a magnetic poleposition according to claim 2 is used as said means for detecting amagnetic pole position.
 7. The method of detecting a magnetic poleposition of a motor according to claim 1, wherein said arbitrary phasedifference is 120 deg., and said arbitrary high frequency is an invertercarrier frequency.
 8. The method of detecting a magnetic pole positionof a motor according to claim 2, wherein said arbitrary phase differenceis 120 deg., and said arbitrary high frequency is an inverter carrierfrequency.
 9. The apparatus for detecting a magnetic pole position for amotor according to any one of claims 3 and 4, wherein said arbitraryphase difference is 120 deg., and said arbitrary high frequency is aninverter carrier frequency.
 10. An apparatus for controlling a motorwherein said apparatus comprises a current controlling apparatus whichsplits a detected current into a pole direction component and a torquecomponent by using said position detected by the apparatus for detectinga magnetic pole position according to any one of claims 3 and 4, whichfeedbacks said components to compare said components with currentcommand values for said pole direction component and said torquecomponent, and which implements a current control so that deviations insaid comparisons become zero.
 11. An apparatus for controlling a motorwherein said apparatus comprises a speed detecting apparatus whichdetects a speed by using said position detected by the apparatus fordetecting a magnetic pole position according to any one of claims 3 and4.
 12. An apparatus for controlling a motor wherein said apparatuscomprises a speed controlling apparatus which compares said speeddetected on the basis of said speed detecting apparatus of the apparatusfor controlling a motor according to claim 11, with a command speed,which implements a speed control so that a deviation in said comparisonbecomes zero, and which outputs a torque command value or a currentcommand value corresponding to a torque command.
 13. An apparatus forcontrolling a motor wherein said apparatus comprises a positioncontrolling apparatus which compares said magnetic pole positiondetected on the basis of the apparatus for detecting a magnetic poleposition according to any one of claims 3 and 4, with a commandposition, which implements a position control so that a deviation insaid comparison becomes zero, and which outputs a speed command value.14. An apparatus for controlling a motor wherein said apparatuscomprises a torque controlling apparatus having: the apparatus fordetecting a magnetic pole position according to claim 9; and the currentcontrolling apparatus according to claim
 10. 15. An apparatus forcontrolling a motor wherein said apparatus comprises a speed controllingapparatus having: the apparatus for detecting a magnetic pole positionaccording to claim 9; the current controlling apparatus according toclaim 10; the speed detecting apparatus according to claim 11, and thespeed controlling apparatus according to claim
 12. 16. An apparatus forcontrolling a motor wherein said apparatus comprises positioncontrolling apparatus having: the apparatus for detecting a magneticpole position according to claim 9; the current controlling apparatusaccording to claim 10; the speed detecting apparatus according to claim11, the speed controlling apparatus according to claim 12; and theposition controlling apparatus according to claim 13.